1. Technical Field of the Invention
The present invention relates to a surveillance system, and more particularly to a surveillance system comprising a plurality of imaging units for respectively taking images of specific images and a plurality of terminal units for respectively displaying thereon the images to be taken by the imaging units to ensure that the specific objects are respectively surveilled through the images respectively displayed by the terminal units.
2. Description of the Related Art
Up until now, there have been proposed a wide variety of surveillance system of this type two typical examples of which are shown in FIGS. 5 and 6.
The first typical example of the conventional surveillance system 300 is shown in FIG. 5 as comprising a plurality of imaging units 310a to 310d for respectively taking images of specific objects to transform the images into image signals, an image signal processing unit 320 for processing the image signals transformed by the imaging units 310a to 310d, and a plurality of terminal units 330a to 330c for respectively displaying the images thereon.
The image signal processing unit 320 includes image signal selecting means 321 for selecting one of the image signals from among the image signals respectively transformed by the imaging units 310a to 310d, image signal encoding means 322 for encoding the image signal selected by the image signal selecting means 321 to an image data, image data compressing means 323 for compressing the image data encoded by the image signal encoding means 322 into a compression data; transmitting means 324 for transmitting the compression data compressed by the image data compressing means 323 to the terminal units 330a to 330c through a network, a central processing unit 325 for controlling the image signal selecting means 321 and the transmitting means 324 to allow each of the terminal units 330a to 330c to receive the compression data.
In the operation of the first typical example of the conventional surveillance system 300, the image signal selected by the image signal selecting means 321 is firstly encoded to the image data by the image signal encoding means 322. The image data encoded by the image signal encoding means 322 is then compressed into the compression data by the image data compressing means 323. The compression data compressed by the image data compressing means 323 is then transmitted by the transmitting means 324 to each of the terminal units 330a to 330c. 
The first typical example of the conventional surveillance system 300 thus constructed as previously mentioned, however, encounters such a problem that the terminal units 330a to 330c cannot simultaneously require two or more different images from among the images taken by the imaging units 310a to 310d, and cannot simultaneously display on thereon the two or more different images by reason that the image signal processing unit 320 is operative to transmit to each of the terminal units 330a to 330c the compression data in association with one of the image to be taken by the imaging units 310a to 310d. 
The second typical example of the conventional surveillance system is shown in FIG. 6 as comprising a plurality of imaging units 410a to 410d for respectively taking images of specific objects to transform the images into image signals, an image signal processing unit 420 for processing the image signals transformed by the imaging units 410a to 410d, and a plurality of terminal units 430a to 430c for respectively displaying the images thereon.
The image signal processing unit 420 includes first image signal selecting means 421a for selecting one of the image signals from among the image signals respectively transformed by the imaging units 410a to 410d, second image signal selecting means 421b for selecting one of the image signals from among the image signals respectively transformed by the imaging units 410a to 410d, first image signal encoding means 422a for encoding the image signal selected by the first image signal selecting means 421a to an image data, second image signal encoding means 422b for encoding the image signal selected by the second image signal selecting means 421b to an image data, first image data compressing means 423a for compressing the image data encoded by the first image signal encoding means 422a into a compression data, second image data compressing means 423b for compressing the image data encoded by the second image signal encoding means 422b into a compression data, compression data recording means 424 for recording the compression data compressed by the first image data compressing means 423a and the compression data compressed by the second image data compressing means 423b, transmitting means 425 for transmitting the compression data to the terminal units 430a to 430c through a network, and a central processing unit 426 for controlling each of the first image signal selecting means 421a, the second image signal selecting means 421b, compression data recording means 424, and the transmitting means 425.
In the operation of the second typical example of the conventional surveillance system 400, the first image signal encoding means 422a is firstly operated to encode the image signal selected by the first image signal selecting means 421a to the image data. The image data encoded by the first image signal encoding means 422a is then compressed into the compression data by the first image data compressing means 423a. The compression data compressed by the first image data compressing means 423a is then recorded by the compression data recording means 424. The image signal selected by the second image signal selecting means 421b is, on the other hand, encoded to the image data by the second image signal encoding means 422b. The image data encoded by the second image signal encoding means 422b is then compressed into the compression data by the second image data compressing means 423b. The compression data compressed by the second image data compressing means 423b is then transmitted by the transmitting means 425 to the terminal units 430a to 430c through the network.
The second typical example of the conventional surveillance system 400 thus constructed as previously mentioned, however, encounters such a problem that the conventional surveillance system 400 is complicated in assembly and thus expensive in production cost, resulting from the fact that the image signal processing unit 420 includes two image signal encoding means and two image data compressing means to have the compression data recording means 424 record the compression data, and to have transmitting means 324 transmit the compression data to the terminal units 430a to 430c. 